The present invention relates to a sputtering target capable of shortening the burn-in time and performing deposition on a wafer or a substrate at a stable speed during sputtering.
Heretofore, the reduction of particles and improvement of uniformity (uniformization of the film thickness and film resistance) were sought by controlling the crystal grain size and crystalline orientation of high-purity tantalum materials in a tantalum sputtering target. Examples of this are described below.
For instance, proposed is technology of providing a tantalum sputtering target, wherein the average crystal grain size is 0.1 to 300 μm, variation of the average crystal grain size according to location is within ±20%, the oxygen concentration is 50 ppm or less, and, with respect to the impurity concentration, Na≦0.1 ppm, K≦0.1 ppm, U≦1 ppb, Th≦1 ppb, Fe≦5 ppm, Cr≦5 ppm, Ni≦5 ppm, and the total content of high-melting metal elements (Hf, Nb, Mo, W, Ti and Zr) is 50 ppm or less. This tantalum sputtering target is able to improve the deposition speed by selectively increasing the plane orientation of {110}, {200} and {211} having a high atom density as the sputtering surface, and improve the uniformity by inhibiting the variation of the plane orientation (Patent Document 1).
Further, proposed is a tantalum sputtering target comprising a crystal structure in which the (222) orientation was preferential from a position of 30% of the target thickness toward the center plane of the target for improving the uniformity throughout the sputtering life (Patent Document 2).
Patent Document 3 proposes a metal product and a sputtering target comprising at least substantially 99.95 wt % of tantalum and a (100) cubic texture of that the surface is substantially uniform, and having a maximum grain size of 50 microns or less. This technology is useful as a metal product having a fine and uniform texture, particularly as a sputtering target.
Further, in order to reduce the particles in the initial stage of sputtering and obtain a uniform film (uniformity), it is important to reduce the surface roughness and eliminate a work-affected layer (residual stress layer) on the surface of the sputtering target. An example of this is shown in Patent Document 4.
Patent Document 4 describes that it is possible to reduce the generation of particles by substantially eliminating the machining defect layer (crushed layer) resulting from minute cracks and missing portions generated during the machining process at least on the surface portion of a sputtering target for a high-melting metal alloy. In order to realize this, Patent Document 4 describes that it is important to refine the finish surface roughness (Ra of 0.5 μm or less), and give consideration to reducing the working steps in relation to the distribution of material defects in order to substantially eliminate the machining defect layer with cracks and dropout holes.
The surface treatment method reduces the abrasive grains and refines the finish surface roughness through the steps of lapping, polishing and mechano-chemical polishing, and thereby reduces the residual stress caused by grinding.
Further, Patent Document 5 describes a sputtering target, wherein the surface roughness (Ra is 1.0 μm or less), the total content of Si, Al, Co, Ni, B and high-melting metal elements excluding the primary components and alloy components as contaminants is 500 ppm or less, the hydrogen content on the surface is 50 ppm or less, and the thickness of the work-affected layer is 50 μm or less. Patent Document 5 further describes that, when necessary, the target is manufactured by precision cutting with a diamond tool.
As described above, cutting work (in particular, diamond finishing-cut) and polishing processing (wet polishing or chemical processing) are performed in manufacturing a sputtering target, and it may be difficult to prevent the generation of nodules even if the surface roughness is adjusted when high deformation is performed. This is assumed to be because when high deformation is performed, the atomic arrangement is disturbed and the angle of the particles discharged during sputtering becomes lower, and even if the surface roughness is low, namely, even if the asperity of the surface is small, it eases adherence of particles to the surface. Thus, it was necessary to keep the thickness of the work-affected layer of the surface 50 μm or less.
If high deformation is performed so that the thickness of the work-affected layer exceeds 50 μm, it is not possible to effectively reduce the number of nodules and particles.
This technology itself is effective. Nevertheless, it requires an extremely long time to completely eliminate the work-affected layer (residual stress layer) of the target surface, and there are problems in low productivity and a waste of materials through cutting and grinding the target thickly.
Further, it is difficult to uniformly polish a large area (for instance, up to around φ450 mm) of a target or the like by chemical polishing such as etching, and the surface gloss often deteriorates by selectively etching the crystal grain boundary. In particular, tantalum having high chemical resistance must be polished with powerful hydrofluoric acid or sulfuric acid, and there is a problem in that the removal of the residual liquid is difficult.
In the sputtering process, a conditioning process referred to as a burn-in is performed while subjecting a dummy wafer to a flow until the initial deposition becomes stable. As with this burn-in process, proposals have been made to perform reverse sputtering after the final processing of the target in order to eliminate the work-affected layer so as to shorten the burn-in time when the target is used in the actual deposition process.
Nevertheless, these various methods require the same level of equipment as a sputtering device for manufacturing semiconductors. Moreover, in these methods, the burn-in time is merely shifted to the target manufacturing process and it does not provide the comprehensive solution for shortening the overall processing time.    [Patent Document 1] Japanese Patent Laid-Open Publication No. H11-080942    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2004-107758    [Patent Document 3] National Publication of Translated Version 2002-518593    [Patent Document 4] Japanese Patent Laid-Open Publication No. H3-257158    [Patent Document 5] Japanese Patent Laid-Open Publication No. H11-1766